Liquid electrostatic developing medium having a mixture of non-esterified tricyclic diterpene carboxylic acid and polyhydric alcohol

ABSTRACT

A LIQUID ELECTROSTATIC DEVELOPER HAVING TONER PARTICLES DISPERSED IN AN INSULATING, NONPOLAR ORGANIC LIQUID CARRIER IS USED FOR THE DEVELOPMENT OF ZINC OXIDE COATED COPY SHEETS AND THE LIKE. A TRICYCLIC DITERPENE CARBOXYLIC ACID OR HEAT BLENDED MIXTURE OF A TRICYCLIC DITERPENE CARBOCYLIC ACID AND A POLYHYDRIC ALCOHOL ABSORBED ON THE TONER PARTICLES ORIENTS THE POLARITY AND CONTROLS THE MAGNITUDE OF THE CHARGE ON THE TONER PARTICLES. SUITABLE ACIDS ARE LEVOPIMARIC ACID, ABIETIC ACID, NEOABIETIC ACID, DEHYDROABIETIC ACID, DIHYDROABIETIC ACID, TETRAHYDROABIETIC ACID, DEXTROPIMARIC ACID, AND ISODEXTROPIMARIC ACID. SUITABLE POLYHYDRIC ALCOHOLS ARE ETHYLENE GLYCOL, TRIETHYLENE GYLCOL, GLYCEROL, AND PENTAERYTHRITOL.

United States Patent LIQUID ELECTROSTATIC DEVELOPING MEDIUM HAVING A MIXTURE OF NON-ESTERIFIED TRI- CYCLIC DHTERPENE CARBOXYLIC ACID AND POLYHYDRIC ALCOHOL Lauren L. Hulse, Lexington, Ky., assignor to Addressograph-Multigraph Corporation, Mount Prospect, Ill. No Drawing. Filed Sept. 1, 1967, Ser. No. 664,957

Int. Cl. G03g 9/04 US. Cl. 252-621 12 Claims ABSTRACT OF THE DISCLOSURE A liquid electrostatic developer having toner particles dispersed in an insulating, nonpolar organic liquid carrier is used for the development of zinc oxide coated copy sheets and the like. A tricyclic diterpene carboxylic acid or heat blended mixture of a tricyclic diterpene carboxylic acid and a polyhydric alcohol absorbed on the toner particles orients the polarity and controls the magnitude of the charge on the toner particles. Suitable acids are levopimaric acid, abietic acid, neoabietic acid, dehydroabietic acid, dihydroabietic acid, tetrahydroabietic acid, dextropimaric acid, and isodextropimaric acid. Suitable polyhydric alcohols are ethylene glycol, triethylene glycol, glycerol, and pentaerythritol.

BACKGROUND OF INVENTION This invention relates to a liquid electrostatic developer and, more particularly, concerns a novel orienting agent 'which controls the polarity and the magnitude of the charge on the toner particles which are dispersed in the developer.

As is Well known in the photoelectrostatic copying art, liquid developers are employed to develop exposed photoelectrostatic copy sheets bearing a latent electrostatic image. Developers of this type comprise an insulating liquid carrier in which are dispersed finely divided colored toner particles. The copy sheet is developed by bringing the surface bearing the latent electrostatic image into contact with the developer, with the charged particles of the developer migrating to the oppositely charged image areas on the copy sheet. In accordance with conventional techniques for formulating liquid developers, an orienting agent is added to the developer. This orienting agent, which is adsorbed by the toner particles, determines the polarity and the magnitude of the particle charge.

SUMMARY OF INVENTION One object of this invention is to provide an improved liquid electrostatic developer capable of producing dense, well defined image areas while leaving the background areas of the copy sheet being developed free of unwanted toner deposits. Another object of this invention is to impart to toner particles an intense electrostatic charge of a positive polarity so that the toner will be strongly attracted to negative image areas. A related object is to provide a developer that is especially well adapted to develop a zinc oxide/binder copy sheet having image areas of a negative polarity.

I have discovered that naturally occurring resin acids, such as tricyclic diterpene carboxylic acids, or the heat blended mixture of a resin acid and a polyhydric alcohol function in liquid electrostatic developers as excellent orienting agents.

As a result of this discovery, there is provided in accordance with this invention an improved electrostatic developer comprising an organic insulating liquid carrier in which are dispersed pigment particles having adsorbed thereon a novel orienting agent consisting of a tricyclic diterpene carboxylic acid or a non-esterified, heat blended mixture of a tricyclic diterpene carboxylic acid and a polyhydric alcohol.

Examples of tricyclic diterpene carboxylic acids suitable for use in accordance with the teachings of the present invention are as follows:

Abietic-type carboxylic acids /0 H3 /C H3 -C H -C H H3 0 H3 H3 C H; Dihydroabietic Acid Tetrahydroabietlc Acid Pimaric-type carboxylic acids CH COOH CH COOH CH=CH3 CH3 H3 0 H H3 CH=CH Dextropimario Acid Isodextropimaric Acid Although in many instances the addition of the tricyclic diterpene carboxylic acid alone is suflicient to improve the density and sharpness of the developed image, it is some times desired to use a heat blended mixture of the acid and a polyhydric alcohol in order to provide even better copy development. Alcohols which can be mixed with the acids are ethylene glyocol, triethylene glycol, glycerol, and pentaerythritol. The acid and alcohol are blended together at a temperature in the range of from about to C., preferably for a period not exceeding 15 minutes to insure against esterification of the acid. Esterification of the acid destroys its orienting properties. Usually only a minor amount of alcohol is employed as, for

example, 5% to 15% by weight of the mixture.

Only a very small amount of the orienting agent of this invention need ordinarily be employed. The usual Weight ratio of pigment particles to agent is generally not more than about 1:4, but frequently less agent can be employed. Only about 0.5 to 10 parts by Weight of the pigment particles and agent together are added to 100 parts by Weight of the carrier.

Suitable toner particles can be selected from a wide variety of inorganic or organic compounds such as, for example, barium sulfate, calcium silicate, zinc oxide, iron oxide, hansa yellow, phthalocyanine blue, phthalocyanine green, carbon black, or mixtures thereof. Toner using a major portion of carbon black is preferred. The particles are preferably ground to a size ranging from about .01 to 20 microns.

Liquid carriers which are suitable for use include nonpolar hydrocarbons, preferably those having a KB below about 28 and a resistivity above ohm-centimeters. Examples of liquid carriers are gasoline, kerosene, turpentine, benzene, carbon tetrachloride, and cyclohexane. A preferred liquid carrier is an isoparifiinic hydrocarbon sold by Humble Oil and Refining Co. under the trade name Isopar H. This hydrocarbon liquid having both a KB below 28 and a resistivity of about 10 ohm-centimeters is particularly well adapted for use as a carrier, since it does not tend to dissolve the zinc oxide/resin binder photoconductive coating of the copy sheet being developed.

I have found that, when the orienting agent is added to developers, the resistivity of the developer is usually reduced. Moreover, when the agent is added in an amount sufficient to place the resistivity of the developer at approximately 10 ohmcentimeters, a marked improvement in print density is usually achieved. This particular phenomenon was commonly noticed when the isoparaffinic hydrocarbon Isopar H was employed as the carrier.

DESCRIPTION OF PREFERRED EMBODIMENTS The following examples serve to illustrate the principles of this invention and should be interpreted in an illustrative rather than limiting sense, since modifications in toner pigments and carrier liquids can be readily made by those skilled in the art.

The above ingredients are blended together to form a paste. The Microlith resinated pigments, manufactured by Ciba Limited, contain approximately 80% by weight of a hydrogenated rosin ester binder resin. Microlith CT is carbon black dispersed in the resin, and Microlith Blue 4GT is phthalocyanine blue dispersed in the resin.

Sixty grams of this paste are cut with 40 milliliters of a solution comprising 50% by weight of Isopar H and 50% by weight of the orienting agent, abietic acid. A half gram of this cut paste is then dispersed in a liter of Isopar H containing 0.40 gram of abietic acid.

The asphalt serves as an auxiliary pigment, and the ethylhydroxyethylcellulose functions as an antismudge agent. The use of the asphalt is optional, and antismudge agents other than ethylhydroxyethylcellulose can be employed. Although it is preferred that the pigments be resinated with the rosin ester resin, nonresinated pigments can also be employed.

The liquid developing medium prepared in accordance with this example, when used to develop a zinc oxide/ binder photoconductive member bearing a latent e ectrostatic image of negative polarity, produces substantially background free dense black image deposits.

EXAMPLE II This example differs from Example I in the substitution of dehydroabietic acid for the abietic acid.

4 EXAMPLE In This example differs from Example I in that in place of the abietic acid a heat blended mixture of dihydroabietic acid and ethylene glycol is used. To prepare this mixture grams of dihydroabietic acid and 10 grams of ethylene glycol are mixed together for about five minutes at a temperature of C.

EXAMPLE IV This example differs from Example I in that in place of the abietic acid a heat blended mixture of tetrahydroabietic acid and ethylene glycol is used. This mixture is prepared in accordance with Example III.

EXAMPLE V This example differs from Example I in the substitution of the heat blended mixture of dihydroabietic acid, 90% by weight, and glycerol, 10% by weight, for the abietic acid.

EXAMPLE VI This example calls for the substitution of the heat blended mixture of tetrahydroabietic acid, 90% by weight, and glycerol, 10% by weight, for abietic acid of Example I.

EXAMPLE VII This example is similar to Example I except that a heat blended mixture of dehydroabietic acid and ethylene glycol is substituted for the abietic acid. The dehydroabietic acid, 90 grams, and ethylene glycol, 10 grams, are heat blended for about five minutes at a temperature of 140 C. to provide the orienting agent.

What is new and desired to be secured by Letters Patent of the United States is:

1. An improved electrostatic liquid developer consisting essentially of an insulating liquid carrier having a resistivity of at least 10 ohm-centimeters having finely divided solid electrostatically attractable pigment-resin particles dispersed therein, and a non-esterified charge orienting agent selected from the group consisting of a nicyclic diterpene carboxylic acid, and a heat blended mixture of a tricyclic diterpene carboxylic acid and a polyhydric alcohol.

2. The developer as defined in claim 1 wherein said acid is selected from the group consisting of levopimaric acid, abietic acid, neoabietic acid, dehydroabietic acid, dihydroabietic acid, tetrahydroabietic acid, dextropimaric acid, and isodextropimaric acid.

3. The developer as defined in claim 2 wherein said alcohol is selected from the group consisting of ethylene glycol, triethylene glycol, glycerol, and pentaerythritol.

4. The developer as defined in claim 1 wherein said mixture comprises a major amount of the acid and a minor amount of the alcohol.

5. The developer as defined in claim 4 wherein said alcohol is present in an amount ranging from about 5% to 15 by weight of the mixture.

6. The developer as defined in claim 4 wherein said acid and alcohol are heat blended at a temperature in the range of from 120 to C.

7. The developer as defined in claim 5 wherein said acid and alcohol are blended together for a period not exceeding 15 minutes.

3. An electrostatic liquid developer consisting essentially of a non-polar isoparaflinic hydrocarbon liquid carrier having a KB below about 28 and a resistivity of about 10 ohm-centimeters;

finely divided elcctrostatically attractable pigment-resin particles dispersed in said carrier having a particle size ranging from about 0.01 to 20 microns; and

a non-esterified charge orienting agent adsorbed by the particles which is added to the carrier in an amount suflicient to place the resistivity of the developer at about 10 ohm-centimeters, said agent being selected from the group consisting of a tricyclic diterpene carboxylic acid and a heat blended mixture of a tricyclic diterpene carboxylic acid and a polyhydric alcohol.

9. The developer as defined in claim 8 wherein said acid is selected from the group consisting of levopimaric acid, abietic acid, neoabietic acid, dehydroabietic acid, dihydroabietic acid, tetrahydroabietic acid, dextropirnaric acid, and isodextropimaric acid.

10. The developer as defined in claim 9 wherein said alcohol is selected from the group consisting of ethylene glycol, triethylene glycol, glycerol, and pentaerythritol.

11. An electrostatic liquid developer consisting essentially of an organic insulating liquid carrier having a resistivity of at least 10 ohm-centimeters having electrostatically attractable colored pigment-resin particles dispersed therein which include a major portion of carbon black, a non-esterificd charge orienting agent adsorbed on said particles selected from the group consisting of a tricyclic diterpene carboxylic acid selected from the group consisting of levopimaric acid, abietic acid, neoabietic 6 acid, dehydroabietic acid, dihydroabietic acid, tetrahydroabietic acid, dextropimaric acid, and isodextrop-imaric acid.

12. The developer as defined in claim 11 wherein the weight ratio of pigment particles to agent is not more than about 1:4, and about 0.5 to 10 parts by weight of particles and agent together are added to 100 parts by weight of the carrier.

References Cited UNITED STATES PATENTS 2,907,674 10/1959 Metcalfe et a1. 25262.l

OTHER REFERENCES Brewster, Organic Chemistry, 1953, p. 769.

GEORGE F. LESMES, Primary Examiner J. P. BRAMMER, Assistant Examiner UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,578,593 Dated May ll, 1971 Invent fl Lauren L! Hulse It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

ABSTRACT OF THE DISCLOSURE "absorbed" should (Llne read adsorbed- Column 3, line 55 "cut" should read diluted 7 Column 3, line 58 "cut" should read -diluted-- Signed and sealed this 2 th day of August 1971.

(SEAL) Atteat:

EIMARD M.FLETCIIER,JR. WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents FORM 90-1050 (10-69) USCOMM-DC bean-Pen fi HTS GOVERNMENT PRINYING Ol'l'OCE: III 0-3Ill-Jll 

